This invention relates to an electric shift apparatus especially suited for use with a motor vehicle having an automatic transmission.
Motor vehicles since their inception having required some manner of gear change mechanism to satisfy the varying torque and speed requirements encountered during a typical duty cycle of a motor vehicle. For many years these gear change mechanisms were manual in the sense that they required an operator input from a shift lever or the like to effect each desired gear change ratio. More recently, so called "automatic" transmissions have become popular in which much of the shifting is done without operator input in response to sensed speed and throttle opening parameters. These automatic transmissions typically include a mode select member positioned on the transmission housing and movable between a plurality of selected positions corresponding to a respective plurality of shift modes within the transmission. The mode select member is typically moved between the several shift positions by a cable or linkage mechanism extending from the mode select member to a suitable gear selector lever located in the passenger compartment of the vehicle. The automatic transmission also typically include valving devices within the transmission to selectively shift the transmission automatically between a plurality of forward shift positions. These valving devices are typically selectively positioned in response to a balancing of various input parameters so as to provide automatic shift points as between the various forward speeds of the transmission with the input parameters typically including throttle position and vehicle speed. It has also become increasing popular in recent years to couple the output of the transmission to a transfer case so as to provide two and four wheel operation for the motor vehicle. The shifting of the transfer case between its two and four wheel modes is typically accomplished by a mechanical lever or linkage.
Various proposals have been made to provide electric control for the various shifting requirements of a modern day motor vehicle transmission assembly. However, these electric control proposals have been disjointed in the sense that they address only one shifting requirement of a transmission assembly. Prior art attempts to electrically control automatic transmissions have also been limited in their commercial success because of the slow or imprecise shifting action or because of excessive warranty and maintenance costs associated with the electric control system.